Abstract: Controlling ion and water transport on a molecular scale is important for applications ranging from industrial water treatment to biomedical separations. Living systems move ions and small molecules across biological membranes by using protein pores that rely on nanoscale confinement effects to achieve efficient and exquisitely selective transport. I will show that carbon nanotube porins — pore channels formed by ultrashort carbon nanotubes assembled in a lipid membrane — can exploit similar physical principles to transport water, protons, and small ions with efficiency that rivals and sometimes exceeds that of biological channels. I will discuss the role of molecular confinement and slip flow in these pores and show how it can enhance water and proton transport efficiency and influence the mechanisms of ion selectivity in these pores. Overall, carbon nanotube porins represent simple and versatile biomimetic membrane pores for building the next generation of separation technologies.